In recent years, in the field of endoscope, a capsule endoscope having an imaging function and a radio communication function has appeared. After a subject swallows the capsule endoscope from the mouth to perform an observation (examination), the capsule endoscope moves within internal organs (within the body cavity) such as an esophagus, a stomach, and a small bowel, following its peristalsis, during the observation period, until when the capsule endoscope is naturally discharged from the body (human body) of the subject. The capsule endoscope sequentially images at a predetermined imaging rate, using the imaging function.
During the observation period when the capsule endoscope moves within the internal organs, image data acquired by imaging within the body cavity by the capsule endoscope is sequentially transmitted to the outside of the subject, by the radio communication function such as radio transmission, and is stored into a memory provided within an external receiving device. When the subject carries the receiving device having the radio communication function and the memory function, the subject can move freely even during the observation period from when the subject swallows the capsule endoscope until when the capsule endoscope is discharged. After the observation, a doctor or a nurse can perform diagnosis by displaying the images of the body cavity on a display unit such as a display, based on image data stored in the memory of the receiving device (see Patent Document 1).
In receiving image data, in general, a receiving device has plural antennas dispersedly disposed at the outside of the subject to receive image signals transmitted from the capsule endoscope, and receives an image signal by selectively switching one antenna having large reception strength. For example, the Patent Document 1 describes a receiving device that switches reception of plural antennas disposed at the outside of the subject, and searches a position of the capsule endoscope within the subject as a signal source of an image signal, based on field strength that each antenna receives.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-19111